This invention relates generally to radio frequency communications and, more specifically, relates to mobile communication stacks.
This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
ACK/NACK acknowledgement/negative acknowledgement
AFE analog front end
ARQ automatic repeat request
AM acknowledged mode
BB base band
BTS base transceiver station
CoMP coordinated multipoint
CPRI common public radio interface
C-RAN cloud RAN
DFE digital front end
DL downlink (from base station to user equipment)
DPD digital pre-distortion
eNB EUTRAN Node B (evolved Node B/base station)
EPC evolved packet core
EUTRAN evolved universal terrestrial access network
FDD frequency division duplexing
HARQ hybrid automatic repeat request
HSDPA high speed downlink packet access
HW hardware
IPsec internet protocol security
IT information technology
L1 layer 1 (physical layer)
L2 layer 2 (data link layer)
L3 layer 3 (network layer)
LTE long term evolution
MAC medium access control
NAS non-access stratum
OBSAI open base station architecture initiative
PDCCH physical downlink control channel
PDCP packet data convergence protocol
PDU protocol data unit
PDSCH physical downlink shared channel
PoC proof of concept
PUCCH packet uplink control channel
PUSCH packet uplink shared channel
RAN radio access network
RF radio frequency
RLC radio link control
ROHC robust header compression
RRC radio resource control
SAP service access point
SCH synchronization channel
SDU service data unit
SON self organized network
SRIO serial rapid input output
SW software
UL uplink (from user equipment to base station)
UM unacknowledged mode
UMTS universal mobile telecommunication system
WLAN wireless local area network
One modern communication system is known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA).
Of particular interest herein are the further releases of 3GPP LTE (e.g., LTE Rel-10, LTE Rel-11) targeted towards future IMT-A systems, referred to herein for convenience simply as LTE-Advanced (LTE-A). LTE-A is specified in Rel-10 (see, e.g., 3GPP TS 36.300 v10.3.0 (2011-03)), further enhancements in Rel-11. Reference in this regard may also be made to 3GPP TR 36.913 V9.0.0 (2009-12) Technical Report 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for further advancements for Evolved Universal Terrestrial Radio Access (E-UTRA) (LTE-Advanced) (Release 9). Reference can also be made to 3GPP TR 36.912 V9.3.0 (2010-06) Technical Report 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Feasibility study for Further Advancements for E-UTRA (LTE-Advanced) (Release 9).
A goal of LTE-A is to provide significantly enhanced services by means of higher data rates and lower latency with reduced cost. LTE-A is directed toward extending and optimizing the 3GPP LTE Rel-8 radio access technologies to provide higher data rates at lower cost. LTE-A will be a more optimized radio system fulfilling the ITU-R requirements for IMT-Advanced while keeping the backward compatibility with LTE Rel-8.
Coordinated multi-point (CoMP) transmission and reception is considered for LTE-A as a tool to improve the coverage of high data rates. In this type of system, multiple geographically separated points and antenna(s) at these points receive signals from or transmit signals to multiple user equipments.
The following summary is merely intended to be exemplary. The summary is not intended to limit the scope of the claims.
In an aspect of the invention, an apparatus is disclosed that includes an interface coupled to an access controller, one or more processors, and one or more memories including computer program code. The one or more memories and the computer program code are configured to, with the one or more processors, cause the apparatus to perform at least the following: converting, in downlink, radio frequency signals received from one or more user equipments into corresponding information on transport channels and converting, in uplink, information on the transport channels into the radio frequency signals suitable to be transmitted to one or more user equipments. The converting includes performing at least operations for a physical layer. The one or more memories and the computer program code are configured to, with the one or more processors, cause the apparatus to perform at least the following: performing functions, in uplink, for a data link layer on the information on the transport channels to determine packet signals and sending the packet signals over the interface to the access controller, and performing functions, in downlink, for the data link layer on packet signals received over the interface to create the information on the transport channels. The functions in downlink include downlink packet scheduling functions and downlink medium access control functions and the functions in uplink include uplink packet scheduling functions. The functions performed for uplink and downlink are some but not all of the functions performed by the data link layer to convert information between transport channels and radio bearers.
In another exemplary embodiment, a method includes converting, in downlink, radio frequency signals received from one or more user equipments into corresponding information on transport channels and converting, in uplink, information on the transport channels into the radio frequency signals suitable to be transmitted to one or more user equipments. The converting includes performing at least operations for a physical layer. The method also includes performing functions, in uplink, for a data link layer on the information on the transport channels to determine packet signals and sending the packet signals over the interface to the access controller, and performing functions, in downlink, for the data link layer on packet signals received over the interface to create the information on the transport channels. The functions in downlink include downlink packet scheduling functions and downlink medium access control functions and the functions in uplink include uplink packet scheduling functions. The functions performed for uplink and downlink are some but not all of the functions performed by the data link layer to convert information between transport channels and radio bearers.
In another aspect, another apparatus is disclosed that includes an interface coupled to an access point, one or more processors, and one or more memories including computer program code. The one or more memories and the computer program code are configured to, with the one or more processors, cause the apparatus to perform at least the following: in downlink, receiving information on radio bearers, performing functions for a data link layer on the information on the radio bearers to determine packet signals, sending the packet signals over the interface to the access point, and performing control plane functions. The functions in downlink for the data link layer include performing packet data control protocol functions. The one or more memories and the computer program code are configured to, with the one or more processors, cause the apparatus to perform at least the following: in uplink, receiving packet signals over the interface, performing functions for the data link layer on the received packet signals to create information on the radio bearers, and performing control plane functions. The functions in uplink for the data link layer include performing packet data control protocol functions, wherein the functions performed for uplink and downlink for the data link layer are some but not all of the functions performed by the data link layer to convert information between transport channels and radio bearers.
In another exemplary embodiment, a method includes, in downlink, receiving information on radio bearers, performing functions for a data link layer on the information on the radio bearers to determine packet signals, sending the packet signals over the interface to the access point, and performing control plane functions. The functions in downlink for the data link layer include performing packet data control protocol functions. The method further includes, in uplink, receiving packet signals over the interface, performing functions for the data link layer on the received packet signals to create information on the radio bearers, and performing control plane functions. The functions in uplink for the data link layer include performing packet data control protocol functions, wherein the functions performed for uplink and downlink for the data link layer are some but not all of the functions performed by the data link layer to convert information between transport channels and radio bearers.
In the attached Drawing Figures:
As described above, CoMP reception is considered for LTE-A as a tool to improve the coverage of high data rates and to increase system throughput. In the macro LTE radio network of today, access points (e.g., remote radio head) and access controllers (e.g., baseband units) are connected via standard interfaces such as CPRI or OBSAI. The entire baseband processing is carried out in the access controllers while there is no baseband processing at all in the access points.
For such architecture, a high speed optical fiber interface (greater than three Gbps, gigabits per second) is required between the access point and access controller. This is not an issue if the access point is installed on top of a mast while access controller is at the foot of mast. However, this becomes a large problem in a cloud-RAN (C-RAN) architecture, where the access point and access controller can be separated by hundreds of meters or even many kilometers.
The C-RAN architecture is mostly impractical for outdoor deployment due to lack of accessible optical backhaul in most countries. Even in an indoor enterprise deployment, most in-building wiring infrastructure can only support up to about 1 (one) Gbps throughput with CAT 5e (category 5, enhanced) cabling.
At the other extreme end of spectrum, femto or enterprise femto devices are used, where there is no access controller at all since all functionalities including baseband processing are performed in the access point. See
Common problems with such highly integrated systems (e.g., home eNB, enterprise femto) include the following: a lack of feature parity with macro eNB; a lack of performance; these are difficult to upgrade to support more advanced features in LTE-Advanced.
Alternatively, some baseband processing could be left in the access points. One problem to solve is to select which functionalities to place in which node (access point or access controller). This is particularly true with respect to the L2 layer (i.e., data link layer), as this layer (as described below) has strict latency requirements.
As stated above, one problem to solve is to select which functionalities to place in which node (access point or access controller). The functionality left in the access controller should be maximized to enable efficient pooling of resources. On the other hand, L2 processing and packet scheduling is latency-critical due to strict HARQ loop timing requirements connected to the physical layer air interface. This would mean that remote deployment of the L2 layer causes strict latency requirements on the interface between the access points and access controllers, leading to an expensive interface. For example, when the access points are located far away from the access controllers, copper is out of consideration and there is a need for optical fiber or microwaves with SRIO interfaces. So the target is to deploy all latency-critical functionality in the access point.
In particular, the latency requirements for the eNB functionality in the downlink HARQ loop are critical. See
The DL HARQ loop 655 shows an example of a HARQ loop, which should meet a latency requirement of 3 ms (milliseconds). The latency requirements for DL HARQ include the following:
Latency requirements for uplink HARQ loop 755 (see
In a typical implementation, the budget for the eNB functionality in both HARQ loops 655, 755 is three ms (milliseconds).
UMTS architecture places RLC and MAC protocols in the RNC and L1 in the Node B. This does not support HARQ. In the HSDPA architecture of UMTS, the HARQ part of MAC is placed in the Node B. In an enterprise WLAN architecture, a similar access point and controller structure has been used from certain vendors. Although the products from the above vendors all use proprietary protocols, an IEEE CAPWAP protocol has been proposed to standardize the split-MAC interface in WLAN. However, each of these architectures still leaves time-critical functions in their respective control elements and still requires high data rates between the control elements and the points providing wireless interactions with client devices.
Before describing the exemplary embodiments of this invention, reference is made to
The UE 10 includes a controller, such as at least one data processor (DP) 10A, at least one computer-readable memory medium embodied as a memory (MEM) 10B that stores a program of computer instructions (PROG) 10C, and at least one suitable radio frequency (RF) transceiver 10D for bidirectional wireless communications with the access point 130 (and the access controller 12) via one or more antennas 10E.
The access controller 12 also includes a controller, such as at least data processor (DP) 12A, at least one computer-readable memory medium embodied as a memory (MEM) 12B that stores a program of computer instructions (PROG) 12C. Additional detail regarding other circuitry in the access controller 12 is described below. The access controller 12 is coupled via a data and control path 13 to the NCE 14. The path 13 may be implemented as an Si interface, as shown in
In this example, the access point 130 includes a controller, such as at least one data processor (DP) 130A, at least one computer-readable memory medium embodied as a memory (MEM) 130B that stores a program of computer instructions (PROG) 130C, and one or more antennas 130E (as stated above, typically several when MIMO operation is in use). The access point 130 communicates with the UE 10 via a link 35. Additional detail about the access point 130 is provided below.
At least one of the PROGs 12C and 130C is assumed to include program instructions that, when executed by the associated DP(s), enable the corresponding apparatus to operate in accordance with the exemplary embodiments of this invention, as will be discussed below in greater detail. That is, the exemplary embodiments of this invention may be implemented at least in part by computer software when executed by the DP(s) 12A of the access controller 12, and/or by the DP(s) 130A of the access controller, or by hardware (e.g., an integrated circuit configured to perform one or more of the operations described herein), or by a combination of software and hardware.
The computer-readable memories 12B and 130B may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, random access memory, read only memory, programmable read only memory, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors 12A and 130A may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multi-core processor architectures, as non-limiting examples.
Now that exemplary apparatus have been described, additional detail about the exemplary embodiments is provided. This invention proposes techniques to re-partition the functionality split between the access point and access controller, which in turn result in a new interface between the two entities.
Turning to
In addition, part of the baseband functionality can be optimized when co-located and merged with the DFE circuitry 510 of the access point 130. One example is the digital pre-distortion.
The access controller incorporates L3 functionality 560 and non time critical part 540 of the L2 functionality 550. Organized in a pool (i.e., of multiple access controllers 12), access controllers 12 are the processing core in C-RAN architecture. Efficient load balancing, fault tolerance and easy upgrade to support LTE-Advanced features can be realized centrally in the access controller pool. In addition, coordinated radio resource management and system wide interference avoidance can be implemented in the access controller 12 which has visibility to many access points 130.
An example of a proposed new interface will typically require (as an example) 150 Mbps (megabits per second) throughput for a 20 MHz 2×2 MIMO FDD-LTE system, which is a magnitude lower than the 3 Gbps required in existing systems. Copper or even wireless backhaul links 15 (see
The exact line where the access point 130 and access controller 12 split depends on design tradeoffs such as latency, implementation complexity, security, and standard protocol availability.
The following four deployments are examples of possible deployments, each having advantages. Reference may be made to
Deployment A (indicated by line 1110-1, which corresponds to interface 555):
The access point 130, in the L2 functionality portion 530, contains the following:
The access controller 12, in the L2 functionality portion 540, contains the following: the PDCP protocols and their corresponding functionalities 605, 610 (respectively).
Non-limiting advantages to this deployment include but are not limited to the following:
Deployment B (indicated by line 1110-2, which corresponds to interface 555):
The access point 130, in the L2 functionality portion 530, includes the following:
The access controller 12, in the L2 functionality portion 540, includes the following:
Non-limiting advantages to this deployment include but are not limited to the following:
Deployment C (indicated by line 1110-3, which corresponds to interface 555):
The access point 130, in the L2 functionality portion 530, includes the following:
The access controller 12, in the L2 functionality portion 540, includes the following:
Non-limiting advantages to this deployment include but are not limited to the following:
Deployment D (indicated by line 1110-4, which corresponds to interface 555):
The access point 130, in the L2 functionality portion 530, includes the following:
The access controller 12, in the L2 functionality portion 540, includes the following:
Non-limiting advantages to this deployment include but are not limited to the following:
The various functionalities shown in
It is noted that the MAC functionalities 625, 630 include but are not limited to the following functions (see 3GPP TS 36.300, section 6.1 and particularly section 6.1.1):
The RLC functionalities 615, 620 include but are not limited to the following functions (see 3GPP TX 36.300, section 6.2 and particularly section 6.2.1):
The PDCP functionalities 605, 610 include but are not limited to the following (see 3GPP TX 36.300, section 6.3 and particularly section 6.3.1):
For the user plane:
For the control plane:
The above examples primarily related to user plane functionality. In addition to user-plane functionality, an eNB 134 and its access controller 12 would also implement control-plane functionality. See
Exemplary advantages of this invention include one or more of the following non-limiting examples:
In additional exemplary embodiments, an apparatus includes means for converting, in downlink, radio frequency signals received from one or more user equipments into corresponding information on transport channels and converting, in uplink, information on the transport channels into the radio frequency signals suitable to be transmitted to one or more user equipments, the means for converting comprising means for performing at least operations for a physical layer; and means for performing functions, in uplink, for a data link layer on the information on the transport channels to determine packet signals and sending the packet signals over an interface to an access controller, and means for performing functions, in downlink, for the data link layer on packet signals received over the interface to create the information on the transport channels, the means for performing the functions in downlink comprising means for performing downlink packet scheduling functions and means for performing downlink medium access control functions and the means for performing functions in uplink comprising means for performing uplink packet scheduling functions, wherein the functions performed for uplink and downlink are some but not all of the functions performed by the data link layer to convert information between transport channels and radio bearers.
In an additional exemplary embodiment, an apparatus includes, in downlink, means for receiving information on radio bearers, means for performing functions for a data link layer on the information on the radio bearers to determine packet signals, means for sending the packet signals over an interface to an access point, and means for performing control plane functions, the means for performing functions in downlink for the data link layer comprising means for performing packet data control protocol functions; and in downlink, means for receiving packet signals over the interface, means for performing functions for the data link layer on the received packet signals to create information on the radio bearers, and means for performing control plane functions, the means for performing functions in downlink for the data link layer comprising means for performing packet data control protocol functions, wherein the functions performed for uplink and downlink for the data link layer are some but not all of the functions performed by the data link layer to convert information between transport channels and radio bearers.
Embodiments of the present invention may be implemented in software (executed by one or more processors), hardware, or a combination of software and hardware. In an example embodiment, the software (e.g., application logic, an instruction set) is maintained on any one of various conventional computer-readable media. In the context of this document, a “computer-readable medium” may be any media or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer, with examples of a computer described and depicted, e.g., in
If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the above-described functions may be optional or may be combined.
Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims below.
It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as recited below in the claims.